The invention relates to an arrangement for receiving TV-signals containing left and right stereo sound signals, a first sound carrier being frequency-modulated by the sum signal (L+R) of the two stereo sound signals and a second sound carrier being frequency-modulated by twice the right stereo sound signal (2R), comprising a first FM demodulator for demodulating the sum signal from the first sound carrier and a second FM-demodulator for demodulating twice the right stereo sound signal from the second sound carrier, a matrix circuit for deriving at least the left stereo sound signal from the sum signal and twice the right stereo sound signal, and a left and a right sound channel for the respective left and right stereo sound signals.
It is known, in the transmission of TV-signals having left and right stereo sound signals, to modulate the first sound carrier by the sum signal (L+R) of the two stereo sound signals and to modulate the second sound carrier by the different signal (L-R) of the two sound signals. This has on the one hand the advantage that monophonic TV receivers which are only capable of receiving and demodulating the first sound carrier, reproduce the sum signal which corresponds to the average between the left and the right stereo sound signals. In addition, this system has the advantage that in a stereo receiver it is possible to recover in a simple manner (by addition and subtraction) the signals L and R and that in the L-R channel of the receiver, several features can be included, such as, for example, a mono-stereo change-over device (by blocking or not blocking the L-R channel), an arrangement for the gradual transition from stereo to mono (by increasing the attenuation in the L-R channel), a spatial-stereo arrangement (by additional amplification of the L-R signal with respect to the L+R signal) and/or a stereo-indication arrangement for indicating actual stereo transmissions.
As described in the German Offenlegungsschrift 28 27 159, such a system has, however, the disadvantage that any correlated interferences present in the two sound carriers find their way into the left sound channel of the receiver only and in order to obviate this disadvantage the German Offenlegungsschrift proposes a system wherein L+R is transmitted over the first sound carrier and 2R is transmitted over the second sound carrier, resulting in correlated interferences being distributed equally over the two sound channels. The receiver disclosed in that German Offenlegungsschrift and described in the opening paragraph comprises a dematrixing circuit, the 2R signal received via the second carrier being halved and the R signal thus obtained being subtracted from the L+R signal which was received over the first carrier. In this way, it is however not possible to realize the advantages of a system in which on the one hand L+R and on the other hand L-R are received.